Compressional wave signaling device



A. c. KELLER ZAW,

COMPHESSIONAL WAVE SIGNALING DEVICE Filed July 2, 1943 3 Sheets-Sheet 1FIG. I

SCREENS [NI/EN r01? AC. KELLER BY Walla} G 714mm! A T TOR/V5) W%?. .A.c. KELLER COMPRESSIONAL WAVE SIGNALING DEVICE Filed July 2, 1943 3Sheets-Sheet 2 FIG. 8

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COMPRESSIONAL WAVE SIGNALING DEVICE Filed July 2, 1943 3 Sheets-Sheet 3INVENTOR A. C. WELLER BY MAM 7M A TTORNEV atented RESSIONAL WAVESIGNALmG DEVICE Arthur C. Keller, Brolle, N. Y., assignor to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation ofNew York Application July 2, 1943, Serial No. $93,177

5 Ella.

This invention relates to compressional wave signaling devices and moreparticularly to high frequency or supersonic submarinesignal-proiectors' and detectors especially adapted for mounting on orfrom the hull of a ship.

One object of this invention is to obtain 'a highly directionalpropagation or response pattern for a submarine signaling device. Morespecifically, one object of this invention is to obtain such a patternwherein all secondary lobes are suppressed to'a level greatly below thatof the primary lobe.

Another object of this invention is to achieve substantiallydistortionless translation of supersonic signals in submarine signalprojectors and detectors.

A further object of this invention is to realize substantially uniformtranslation of signals and sharp directionality throughout a widefrequency band in submarine signaling devices.

Still another object of the invention is to improve the efficiency ofcompressional .wave signaling devices.

In one illustrative embodiment of this invention, a submarine signalingdevice operable as either a projector or detector of supersonicsubmarine signals comprises a streamlined housing adapted to be mountedfrom or on the hull of a ship and a signal translating device rotatablymounted within the housing. In one form, the

translating device includes a group of piezo-electric crystals arrangedand graded as to power capacity to produce a maximum response along theaxis normal to the face. of the translating device and constructed andmounted to have a maximum sensitivity at a prescribed frequency, thefrequency at which the device is to be utilized, if singlefrequencyoperation is intended, or the highest frequency in the band to betranslated, if band frequency operation is intended or desired. 4

In accordance with one feature of this invention, the crystals arearranged in coordinately symmetrical rows with their radiating orreceiving faces coplanar and the crystal dimensions and spacings arecorrelated in relation to a preassigned frequency whereby a highlydirectional propagation or reception pattern is realized and a great andsubstantially optimum suppression of secondary lobes in this pattern isobtained.

In accordance with another feature of this invention, the housingisprovided with a large area portion or window opposite the signaltranslating device, of an extent sufficient to allowscanning throughouta large angle by rotation of the translating device, and this portion isconstructed so as to withstand great hydrostatic pressures and forceswithout yielding or vibration and to be capable of allowing transmissiontherethrough of high frequency and supersonic compressional wavesignals, that is signals having a frequency of the order of 10kilocycles and higher, without substantial attenuation and withuniformity independent of the angle of incidence of the signal wavesthereon. Means are provided within the housing for preventing unduereflection of signal waves which pass through the window and are notreceived by the device and other means are provided for shielding thetranslating device from extraneous signals emanating from sourcesoutside of the angular range through which the device is adapted toscan, whereby distortion of the signals by reflection effects orextraneous signals or noises is prevented. In one construction the meansnoted are fabricated as a unitary assembly with a transverse bulkheadpositioned adjacent the ends of the sonically transparent window, thereflection preventing means comprises an attenuator pad capable ofabsorbing the energy of compressional waves incident thereon and thismay be associated with a shielding means comprising a cellular membercapable of reflecting compressional waves which impinge upon it.

The invention and the above-noted and other features thereof will beunderstood more clearly and fully from the following detaileddescription with reference to the accompanying drawing in which:

Fig. 1 is a side elevational view of a supersonic submarine signalingdevice illustrative of one embodiment of this invention, portions of thehousing being broken away and a part of the bulkhead assembly beingillustrated in section to show details of construction;

Fig. 2 is a top view of the signaling device illustrated in Fig. 1,portions of the housing being broken away and the bulkhead assembly andthe translating device being shown partly in section;

Fig. 3 is a front view of the translating device included in thesignaling device shown in Figs; 1 and 2, the major portion of the frontwall of the translating device being broken away;

Fig. 4 is a side view, mainly in section of the translating deviceillustrated in Fig. 3;

Fig. 5 is a sectional View along plane 5--5 of Fig. 2 with a portion ofthe bulkhead assembly broken away to show details of the assembly; and

Figs. 6 and 7 are diagrams showing typical directional patterns for asubmarine signaling device-of the construction illustrated in Figs. 1

and 2.

Referring now to the drawing, the submarine signaling device illustratedin Figs. 1 and 2 comprises a rigid housing of streamlined configuration,as shown clearly in Fig. 2, the outer surfacesorwalls of which are of amaterial, such as stainless steel, resistive to the corrosive action ofsea water. The housing may be fabricated as a single element or may bedefined by an upper dome portion Ill and a lower inverted domeshapedportion, designated as ii as a whole, the two portions having juxtaposedflanges l2 joined to one another, together with an interposed washer It,by bolts i3. The signaling device is adapted to be supported from a wall15 of the hull of a ship as by a hollow coupler assembly i6.

The lower dome portion il comprises a base wall I! and a body l8, bothof relatively thick material, e. g. t a inch steel, secured to oneanother as by welding, the body i8 having a large I area cut away toreceive a window structure highly transparent to compressional waveenergy. The window structure includes a framework IQ of expanded metal,for example stainless steel, the openings in which constitute of theorder of '70 to 80 per cent or more of the total area of the framework,and a thin steel sheet 20, for example about 20 mil stainless steel,secured to the framework l9. Advantageously, the expanded metalframework is relatively thin, and the sheet 20 is secured, as bywelding, to each intersection of the,element of the framework. Suchconstruction provides a window through which compressional wave energywill pass with substantially negligible attenuation and minimizesreflections from the dome window and provides also a rigid window ofgreat strength which not only will withstand great hydrostatic pressuresbut also wlllnot introduce extraneous vibrations due to forces actingthereon even when the ship on which the device is supported is travelingat relatively high speeds, e. g. of the order of 20 or more. knots. Thesmall thickness of the expanded metal framework and the large ratio ofthe openings therein to the total window area assure only very smallreflection of compressional waves incident upon the window. Further,

the impedance of the window to sound waves is substantially independentof the angle of incidence of the compressional waves thereon.

Mounted within the lower dome portion ll well toward the forward endthereof and aligned with the window I9, 20 is a signal translatingdevice including a water-tight housing 2| which is mounted on arotatable support 22 the driving shaft 23 for which projects into theinterior of the ship. The housing 2| includes a sound transparent wallor window 24 of suitable material, such as commercially available formsof rubber, thin steel or suitable plastics having substantially the samedensity and impedance to the transmission of supersonic compressionalwave energy as sea water. The unit of the signal translating device, asshown clearly in Figs. 3 and 4,.comprises a foundation plate 25, forexample of metal, which is supported in the housing 2i by four brackets26 and 21 bolted to the plate 25 and secured to the base wall 28 of thehousing 2i and a mounting bar 29 by suitable machine screws 30.Advantageously, resilient, e. g. rubber, spacers 3| are provided betweeneach bracket and. the wall or bar to which it is secured to permitlimited expansion and contraction of the plate and 4 to insulate thecrystal structure from ship vibrations and noises.

Secured to the face of the plate 25 toward the wall 24 is a group ofsquare piezoelectric crystals 32, each of which may be constituted oftwo or more 45-degree Y-cut Rochelle salt slabs joined together and,connected electrically in parallel and which is secured to the plate 25by an insulator detail shown at 33 in Fig. 3, cemented or fastened tothe crystal and plate.

As shown clearly in Fig. 3, the several crystals are arranged in lateraland longitudinal rows; the two or four end crystals in each row arecomposed of two slabs and the intermediate crystals are composed of fourslabs. Each row is symmetrical with respect to the lateral orlongitudinal axis of the entire crystal group and, as will be apparent,the group approximates a, circular array or blanket of crystals. Onehalf the crystals, for example all those to the left of the longitudinalaxis :c.'c in Fig. 3, are connected electrically in parallel byconductors 34 and bus wires 35 leading to terminals 36A and the othercrystals, that is, those to the right of the axis :c-a: in Fig. 3, areconnected electrically in parallel by similar leads 34 and bus wires 35leading to terminals 36b. Leading-in conductors 31, connected to theterminals 35a and 3%, enable operation of each half of the crystalsseparate from the other half or operation of all the crystals inparallel.

Because of the two slab construction of the outer or end crystals ineach row, these crystals have twice the impedance and are capable ofradiating one-quarter the power of the intermediate crystals. Whenallthe crystals are energized in parallel, the propagation pattern of thetranslating device is highly directional, approximately a cone, forexample of an included angle of the order of 23 degrees at 24 kilocyclesabout an axis normal to the faces of the plate 25 and passing throughthe center of the crystal group.

Secured to the other or rear face of the plate 25 or integral therewithare a plurality of backing blocks or resonator members 38, one for eachof the crystals 32 and in alignment therewith. In another construction asolid resonator of suitable length for each half of the crystals may beused. The backing blocks 38 advantageously are of a length substantiallyequal to one quarter the wavelength of the frequency to be translated,or of the mid-band frequency to be translated if the device is intendedfor band frequency operation, and the height of the crystals 32, that isthe dimension thereof normal to the plate 25, likewise is madesubstantially equal to one quarter wavelength of this frequency wherebyvibrational nodes are established substantially at the plate 25 and ahigh efficiency is obtained. Slight differences in the crystal lengthand resonator length may be used to further broaden the frequency band.

It has been found that orientation of the faces of the crystal slabs,the dimensions of the crystals and the spacing thereof are highlyimportant fa:-

tors determining the amplitude of the secondary lobes appearing in thedirective pattern of the translating device. Particularly, it has beenfound that if the major faces of the crystal slabs are parallel to theaxis about which the translating device is rotatable, that is parallelto the :c-x axis as in Fig. 3, a substantial reduction, of the order of10 decibels, in the first secondary lobe is obtained as compared with aconstruction wherein the .slab faces are normal to this axis.

Further, a marked and optimum suppression of this secondary lobe isrealized when the width of each crystal 32 is equal to of the order of0.4

found to enable realization of excellent cancellation when lobecomparison or beating deviation indication operation is utilized withthe device. In this case, as is understood, the two halves of the groupof crystals, that is those to the left and right of the :ra: axis inFig. 3, are operated 180 degrees out of phase after the sound sourc hasbeen located with all the crystals operated in phase, to locate thesound source with respect to one side or the other of the zero axis,that is, the axis normal to the faces of the plate 25. The efflcacy ofthe translating device in side lobe comparison operation is measured bythe cancellation obtained along the zero axis. Operation with phasedifferences between the halves of values other than 180 degrees are alsopossible.

The features noted in the two preceding paragraphs will be appreciatedfrom the typical directional patterns shown in Figs. 6 and 7. Fig, 6shows the pattern when all the crystals are operated in phase and, itwill be apparent, the greatest secondary lobesS are substantially 20decibels down from the primary lobe P, The patternis essentially thesame for both projecting and detecting. Fig. 7 shows the directionalpattern .when the two halves of the crystal group are operated 180degrees out of phase, the two halves of the pattern on opposite sides ofthe zero axis being the main portions of the pattern for the respectivehalves of the crystal group. As is apparent from Fig, 7, thecancellation obtained on the zero axis is substantially 30 decibels ormore so that the sound source can be located accurately as on one sideof the other of this axis.

Mounted rearwardly of the backing blocks or resonators 38 is anattenuator or absorber which comprises a plurality of fine mesh metallicscreens llll, adjacent screens being separated in fixed space relationby spacers 4!. The screens may be of 100 mesh steel screens of 4 milwire and the spacers ti may be sheets of steel expanded metal of theorder of 100 mils thick and the openings in which constitute of theorder of 70 to 80 per cent or greater of the total area. The screens andspacers are mounted in pile-up fashion upon a frame 42 which is securedto inner walls of the housing 2| by brackets 43. The housingti isfilled, as by way of a port I44, with a gasfree viscous fluid, such ascastor oil, having substantially the same characteristics for thetransmission of supersonic compressional wave energyas sea water, It ispossible to chang the frequency band by using a liquid which results insome impedance mismatch. The attenuator or absorber immersed in thefluid serves to absorb much of the nergy of waves projected rearwardlyfrom the crystal and resonator assembly and thus prevents reflection ofsuch waves to the crystal and resonator assembly and, hence, distortionof the signals translated by the assembly. Similarly this screenassembly reduces the rear response when the instrument is operated as adetector.

A bulkhead 44, for example a steel plate welded at its sides to the body3, is mounted in the lower dome portion I I at a region adjacent theends of th window l9 and 20 and supports a reflecting pad and anattenuator or absorbing pad. The attenuator or absorbing pad, as shownmost clearly in Fig. 5, comprises a pile-up of fine mesh screens 45 andexpanded metal spacers 50, similar to the attenuator 40, M, which ismounted within a housing 46, the front wall 41 of which is of a soundtransparent material, such as commercially available forms of rubber,capable of transmltting supersonic compressional wave energytherethrough without substantial attenuation. The housing 46 is filledwith a gas-free fluid, such as castor oil, so that much of the energy ofwaves incident upon the wall 41 is absorbed by the attenuator andreflection of such waves is prevented.

The reflecting pad comprises a body 48 of cellular material, such assponge or multicellular rubber, which is enclosed in a water-tighthousing constituted. by the bulkhead 44 and a metallic cover 49 boltedthereto. Alternatively, the pad may be enclosed in. a sealed housingsecured to the bulkhead. It is effective to reflect substantially allsupersonic. waves incident thereon and thus effectively screens thetranslating device from signals emanating from sources rearwardly of thewindow I9, 20.

When the submarine signaling device is in use, the housing l0 II isfllled with sea water as by way of the top of the upper dome. When thedevice is operated as a detector compressional waves incident upon thewindow I9, 20 are transmitted to the crystals 32 without substantialattenualtion due to the high transparency of the windows i9, 20 and 24to such waves. and the transmission characteristics of the sea waterfilling of the housing Ill, II and the fluid filling of the housing 2|.Because of the sharply directive property of the signal translatingdevice, the direction of the source of the signals detected may belocated to a high degree of accuracy by rotating the translating deviceuntil a maximum response is obtained therefrom. Inasmuch as th windowi9, 20- is of large extent, for example about degrees on either side ofthe longitudi nal axis of the housing I0, I I, the device can scan overa large angle, e. g. about 2'70 degrees.

It is to be noted especially that signals are detected withsubstantially negligible distortion. The location of the signaltranslating device well forward in the housing portion ll places thedevice at a positive pressure area inasmuch as at the region forward ofand adjacent the device the width of this housing portion is increasing.At this region, water turbulence and cavitation are small. Hence, noisesdue to turbulence and cavitation are small and a high signal to noiseratio is obtained. The window i9, 20 is of great strength and rigidityand will not vibrate even when the ship on which the signaling device ismounted is traveling at high speeds and, as previously noted, is highlytransparent to supersonic signals so that signals are passedtherethrough without distortion. compressional waves incident upon thewindow l3, 20 at such angle as not to pass directly to the window 24either pass directly through the window I9, 20 and into the sea or aresubstantially completely absorbed by the attenuator pad M, M. Reflectionefiects in the translating device itself are prevented by the attenuator40, M as pointed out heretofore. Extraneous signals originating to therear of the housing I0, I I, for exampe at the propeller of the shipupon which the signaling device is mounted, are substantially completelyreflected by the reflector pad 48, 69.

In some cases, particularly where moderate vibrations of the resonators38 occur, the directional response pattern of the device may includea180 degree lobe of appreciable magnitude. Such a lobe may besubstantially suppressed by providing a reflecting member, for example athin sheet of cellular material such as cork or a combination of corkand rubber, between the attenuator 40 and the rear of the housing 2|.

It may be noted further that devices of the construction shown anddescribed are characterized by a high efliciency, and a wide band width,of the order of 5 to 6 kilocycles, when operated'as echo rangingdevices. That is, throughout this band, substantially equal over-allresponse for the system is realized throughout a range of frequencies. Awider band, e. g. of the order of 20 kilocycles may be obtained at somesacrifice in I efliciencyj The beam width, which may be measured astheincluded angle between points on the main lobe of the directionalpattern 10 decibels down from the maximum, varies with the frea widefrequency range of uniform response withsharp directionality is realizedin ,devices constructed in accordance with features of this invention.Similar uniformity of power propagation and directionality are obtainedalso if the signaling device is utilized as a supersonic signalprojector.

Reference is made to the application Serial No. 470,807, filed December31, 1942, of Arthur C. Keller and the applicationSerial No. 470,837,filed December 31, 1 942, of Warren P. Mason wherein certain features ofthe sonically transparent window of the housing, and the attenuator padsrespectively are claimed.

Although a specific embodiment of this invention has been shown anddescribed, it will be understood that it is but illustrative and thatvarious modifications may be made therein without departing from thescope and spirit of this invention as defined in the appended claims.

-What is claimed is:

1. A compressional wave signaling device comprising a housing includingan elongated body portion, said portion having a window transparent tocompressional waves and extending over the front end thereof andrearwardly from said end, a signal translating device mounted withinsaid portion adjacent said front end thereof, a compressional .waveenergy absorbing element mounted within said portion adjacent the rearextremities of said window, and compressional wave reflecting meansmounted within said portion rearward of said absorbing element.

' 2. A submarine signaling device comprising a stream-lined housing, atransverse bulkhead mounted within said housing to the rear of the 7center thereof, said housing having a portion transparent tocompressional waves and extending over the front end of said housing andrearwardly to adjacent said bulkhead, a signal translating devicerotatably mounted within said housing adjacent the front end thereof andopposite said portion, a compressional wave attenuator pad mounted onthe face of said bulkhead toward said translating device, and acompressional wave reflecting element mounted on the opposite face ofsaid bulkhead.

3. A submarine signaling device in accordance with claim 2 wherein saidsignal translating device comprises a housing having a wall portiontransparent to supersonic compressional waves, a supersoniccompressional wave translating unit within said second housing andopposite said wall portion, and compressional wave energy absorbingmeans within said second housing and to the side of said unit remotefrom said wall portion.

4. A submarine signaling device in accordance with claim 2 wherein saidsignal translating device comp 8- ng having a wall portion transparentto supersonic compressional waves,

a plate opposite said wall portion, a plurality of a piezoelectriccrystals mounted on the face of said plate toward said wall portion, acompressional wave attenuating pad opposite the other face of saidplate, and a fluid filling for said second housing having substantiallythe same transmission characteristics as. sea water for supersonicsignals.

5. A submarine signaling device comprising a streamlined housingincluding a body portion having a window transparent to compressionalwaves and extending over the front end of said portion and rearwardlybeyond the center thereof, said window comprising a thin, rigidframework of expanded metal and a thin steel sheet covering saidframework and intimately joined thereto, a second housing rotatablymounted within said first housingadjacent said front end and oppositesaid window, said second housing having a wall portion opposite saidwindow and transparent to compressional waves, a signal translating unitwithin said second housing and opposite said wall portion, compressionalwave I energy absorbing means within said second housingopposite theside of said unit remote from said wall portion, a compressional waveenergy attenuator pad extending transversely of said first housing andmounted therein adjacent the ends of said window, and a compressionalwave reflector mounted within'said'flrst housing rearwardly of saidattenuator.

ARTHUR C. KELLER.

REFERENCES CITED The following references are of record in the flle ofthis patent:

4 UNITED STATES PATENT 620,484 German Oct. 22, 1935

